Which technique is useful for colouring a sunset sky?

Correct answer: Smooth blending of warm colours

A sunset sky is commonly represented by related warm hues such as yellow, orange, and red changing gradually across the sky. Smooth blending helps one colour merge into the next and avoids distracting hard bands. Therefore option C is correct. A black outline, isolated dots, or leaving the paper blank cannot show the atmospheric colour transition that gives a sunset its characteristic appearance. The colours should be applied gently and blended before the paint dries too much.